Here be a sample post with a custom background image. To utilize this “feature” just add the following YAML to a post’s front matter.

image:background:filename.png

This little bit of YAML makes the assumption that your background image asset is in the /images folder. If you place it somewhere else or are hotlinking from the web, just include the full http(s):// URL. Either way you should have a background image that is tiled.

If you want to set a background image for the entire site just add background: filename.png to your _config.yml and BOOM — background images on every page!

Syntax highlighting is a feature that displays source code, in different colors and fonts according to the category of terms. This feature facilitates writing in a structured language such as a programming language or a markup language as both structures and syntax errors are visually distinct. Highlighting does not affect the meaning of the text itself; it is intended only for human readers.1

Video embeds are responsive and scale with the width of the main content block with the help of FitVids.

Not sure if this only effects Kramdown or if it’s an issue with Markdown in general. But adding YouTube video embeds causes errors when building your Jekyll site. To fix add a space between the <iframe> tags and remove allowfullscreen. Example below: